In multisensor signal processing environments, such as those employed for imagery signal generation, statistical signal processing schemes are used to enhance the electrical signals that are representative of a desired target optical image and to suppress unwanted signals (noise) which represent background clutter. Commonly included within such schemes as a mechanism for accomplishing target/background separation is a data value selection filter, such as a median filter, that operates to extract a preestablished electrical amplitude value from a set of amplitude values that constitute an image, or some portion (window) thereof, as viewed by the opto-electronic transducer array of the optical imaging system. Typically, in this type of imaging system, the filtered image of the target is produced by eliminating or blanking most of the electrical noise which has a value significantly different than a prescribed value (e.g. the median) as established by the filter.
In copending application Ser. No. 393,331, now U.S. Pat. No. 4,513,440, filed June 29, 1982, entitled "Hardware Median Filter" by D. J. Delman, and assigned to the Assignee of the present application, there is described an improved configuration for a digital hardware median filter that enjoys substantially reduced hardware and signal processing complexity over conventional filtering mechanisms through a two-dimensional pipelined architecture that is capable of operating on a large number of imagery data inputs to produce a digital output word representative of the median value of the total set of imagery data applied to the filter.
For this purpose the filter contains a set of line buffers to which (pixel) data for an image of interest is applied, to define a segment or window within the overall image. This multibit data is then propagated through a set of n-pipelined filter processing sections (n being the number of bits/pixel). Each filter section examines a particular bit position of the windowed imagery data and decides which bit (zero or one) represents the majority bit for that bit postion. As a result of this decision the data bits of the stored pixel data are either simply transferred to the next downstream section, or they are converted to all ones or all zeros and then passed on to the next downstream section. The bit value that has been determined to be the majority value for that particular bit position is designated as the corresponding bit of the median value and temporarily buffered. After all the bit positions have been processed, the buffered, decided-upon bits for the respective bit positions are combined to produce an output (word) representative of the median value of all the pixels in the window.